Correlational versus Causal Theories In considering the status of physiological
statements about consciousness, it is important to distinguish two different
sorts, which we will callcorrelationalandcausal. Correlational statements con-
cern what type of physiological activity takes place when conscious experiences
are occurring that fail to take place when they are not. Our hypothetical ex-
amples in terms of a specific cortical location, a particular neurotransmitter, or
a particular rate of firing are good examples. The common feature of these
hypotheses is that they are merely correlational: They only claim that the des-
ignated feature of brain activity is associated with consciousness; they don’t
explain why that association exists. In other words, they provide no causal
analysis of how this particular kind of brain activity produces consciousness.
For this reason they fail to fill the explanatory gap that we mentioned earlier.
Correlational analyses merely designate a subset of neural activity in the brain
according to some particular property with which consciousness is thought to
be associated. No explanation is given for this association; it simply is the sort
of activity that accompanies consciousness.
At this point we should contrast such correlational analyses with a good
example of a causal one: an analysis that provides a scientifically plausible
explanation of how a particular form of brain activity actually causes conscious
experience. Unfortunately, no examples of such a theory are available. In fact,
to this writer’s knowledge, nobody has ever suggested a theory that the scien-
tific community regards as giving even a remotely plausible causal account of
how consciousness arises or why it has the particular qualities it does. This
does not mean that such a theory is impossible in principle, but only that no
serious candidate has been generated in the past several thousand years.
A related distinction between correlational and causal biological definitions
of consciousness is that they would differ in generalizability. Correlational anal-
yses would very likely be specific to the type of biological system within which
they had been discovered. In the best-case scenario, a good correlational defi-
nition of human consciousness might generalize to chimpanzees, possibly even
to dogs or rats, but probably not to frogs or snails because their brains are
simply too different. If a correlational analysis showed that activity mediated
by a particular neurotransmitter was the seat of human consciousness, for ex-
ample, would that necessarily mean that creatures without that neurotrans-
mitter were nonconscious? Or might some other evolutionarily related neural
transmitter serve the same function in brains lacking that one? Even more
drastically, what about extraterrestrial beings whose whole physical make-up
might be radically different from our own? In such cases, a correlational analy-
sisisalmostboundtobreakdown.
An adequate causal theory of consciousness might have a fighting chance,
however, because the structure of the theory itself could provide the lines along
which generalization would flow. Consider the analogy to a causal theory of
life based on the structure of DNA. The analysis of how the double helical
structure of DNA allows it to reproduce itself in an entirely mechanistic way
suggests that biologists could determine whether alien beings were alive in the
same sense as living organisms on earth by considering the nature of their mo-
lecular basis and its functional ability to replicate itself and to support the
organism’s lifelike functions. An alien object containing the very same set of
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